Leg Amputation

"If a horse needs an amputation or he's not going to live, that's not much of a choice," began Ric Redden, DVM, founder of the International Equine Podiatry Center and host of the 2003 Bluegrass Laminitis Symposium, in a presentation on Jan. 18. "Horses with catastrophic injury or disease of the lower limb are most often euthanized as there is irreversible vascular, soft tissue, and bone damage. Amputating the limb well above the dysfunctional area and fitting the horse with a prosthesis is a viable option. This is what being a vet is all about--looking at an animal that wants to live and fixing him."

Selecting a Case

The ideal candidate for amputation is a young horse with catastrophic laceration and/or fracture of the hind limb, where the injury is no more than four weeks old, Redden said. Horses seem to handle hind limb amputation better than fore limb amputation "possibly due to weight distribution and the constant twisting load placed on the front end that is not imposed on the rear limb," he added.

"Individuals presented with only unilateral (one front or hind limb) involvement, without impending signs of contralateral limb (the other front or hind limb) laminitis, have all been successful attempts," he reported. "Five cases remain productive and happy, with the longest case now approaching 11 years and the most recent case six months. One stallion has successfully covered his mares for six years, and one mare has for three years produced embryos which have been successfully harvested."

Less ideal candidates are those with chronic septic joints of more than eight weeks duration, chronic forelimb injury or disease, and cases of unilateral injury with contralateral limb laminitis.

Redden has not yet had tried to amputate a limb of a racehorse with a catastrophic fracture, but believes that because of their young age and fitness, they would be good candidates for amputation rather than euthanasia. When horses are catastrophically injured on the track, many veterinarians euthanize them because they appear to be suffering. But, following the extreme activity and excitement of a race, "They all look exhausted and strung out," he said. "Don't use that as your justification for euthanasia. Cool the horse out and take him to the hospital--the decision doesn't have to be made right now. You can't talk about options after you kill the horse."

Phantom Pain

"Phantom pain (pain that seems to originate where the amputated limb used to be) in the horse may be for real," said Redden. "My most recent case, a Quarter Horse mare, has a healthy stump, but apparently has phantom pain due to years of pain from osteomyelitis (bone inflammation) associated with complicated, chronic, unilateral laminitis. She'll be sound as a dollar on the prosthesis some days, and other days she won't touch it to the ground."

Amputation Procedure

"The procedure is quite simple, requires very few surgical tools, and can be performed in most any location," Redden explained. “Using a sling for induction (of anesthesia) and recovery certainly reduces the risk of injury during recovery. The sling must be used for the second cast and several prosthesis changes until the horse has learned to stand unaided by the sling. This might take four to five months. They learn to deal with this, but you have to be game--they might fall on you while they're learning.

"When the foot and coffin joint are involved, I try to leave P1 (the long pastern bone, or first phalanx) and the germinal centers of the coronary groove, digital cushion, and frog," he continued. "Provided these structures remain vitalized, they can be brought up over the end of P1, and sutured to the existing tendon and skin…providing the stump with a tough pad that seems to serve the horse well." This procedure--in effect--allows frog and sometimes hoof wall tissue to grow over the end of the stump, which is much tougher and more able to withstand weight bearing on a prosthesis than normal skin.

If the amputation site is higher on the leg, Redden prepares a foot on the opposite end of the horse with a hospital plate. This foot will be used to harves a small "donation" of germinal frog tissue; once the stump has healthy granulation tissue at two to three weeks post-amputation, the donated frog tissue will be cut into small pieces and implanted throughout the stump. "All cases treated in this fashion have grown a zone of cornified horn," he said. "Some have wall tubules with frog tissue, others just frog tissue. The results have been very stimulating and demand further research.

Post-Operative Care

Following the amputation, transcortical pins are placed through the cannon bone above the amputation site, and a cast is built around the pins for weight bearing. The stump is thus not loaded and better able to heal. "It's important to keep the equipment cool, as thermal necrosis (tissue death from heat) when drilling the holes in the cannon bone is a concern,” Redden said. “The transcortical cast provides pain-free post-op care for three to seven weeks. Once microfractures form around the pins, they must be removed and the stump loaded. The temporary prosthesis can be made in a typical shop using a variety of materials. I prefer one-quarter-inch aluminum plate to form the stump for lower amputation. The higher amputations must have adequate leg extension that can be made with aluminum pipe, PVC for lighter horses, or even wood. The goal is simply to replace leg length and secure it to the limb so it doesn't twist or fall off. You need a non-friction base--if the base won't slide, it torques the pins and can break the bone."

He also recommended that the opposite foot be protected with his Ultimate shoe, which is a cuffed wedge shoe designed to decrease the force of the deep digital flexor tendon and thus avoid supporting limb laminitis.

"If you have a candidate, please call me and I will do all I can to help you assess the case and walk you through each step of the procedure," he concluded. (Dr. Redden can be reached via his web site at www.nanric.com.)

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